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From:   Yu Zhao <yuzhao@google.com>
Date:   Thu, 14 Sep 2023 11:46:35 -0600
Message-ID: <CAOUHufY+7j1L37c1RvCBdkx36qyNZYOBuZa_+GAA4j=9vKzwWA@mail.gmail.com>
Subject: Re: [PATCH] mm: mglru: fix add unevictable folio to lruvec->lists
To:     Zhiguo Jiang <justinjiang@vivo.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, opensource.kernel@vivo.com
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On Thu, Sep 14, 2023 at 8:08=E2=80=AFAM Zhiguo Jiang <justinjiang@vivo.com>=
 wrote:
>
> The unevictable folio is not supported to add to lruvec->lists
> in lruvec_add_folio().
>
> So use lruvec_add_folio_tail() instead of lruvec_add_folio()
> to add unevictable folio to lruvec->lists in sort_folio().
>
> Signed-off-by: Zhiguo Jiang <justinjiang@vivo.com>
> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>  mode change 100644 =3D> 100755 mm/vmscan.c
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 661615fa709b..a15e45632034
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4237,7 +4237,7 @@ static bool sort_folio(struct lruvec *lruvec, struc=
t folio *folio, struct scan_c
>                 success =3D lru_gen_del_folio(lruvec, folio, true);
>                 VM_WARN_ON_ONCE_FOLIO(!success, folio);
>                 folio_set_unevictable(folio);
> -               lruvec_add_folio(lruvec, folio);
> +               lruvec_add_folio_tail(lruvec, folio);
>                 __count_vm_events(UNEVICTABLE_PGCULLED, delta);
>                 return true;
>         }

NAK.

lruvec_add_folio()
{
        ...

        if (lru !=3D LRU_UNEVICTABLE)
                list_add(&folio->lru, &lruvec->lists[lru]);
}

lruvec_add_folio_tail()
{
        ...

        /* This is not expected to be used on LRU_UNEVICTABLE */
        list_add_tail(&folio->lru, &lruvec->lists[lru]);
}

struct page {
        ...
                        union {
                                struct list_head lru;

                                /* Or, for the Unevictable "LRU list" slot =
*/
                                struct {
        ...
}